Charged Particle Beam Device and Method for Controlling Charged Particle Beam Device

The present invention relates to a charged particle beam device and a method for controlling the charged particle beam device.

When a specimen is observed using a charged particle beam device such as a scanning transmission electron microscope (STEM) and a transmission electron microscope (TEM), an image corresponding to a specimen structure projected in an orientation along which an electron beam is emitted is acquired. Focusing on an interface portion where two different substances are in contact with each other, a position of a boundary between the substances can be clearly confirmed in an observation image in a state where the interface is parallel to an emission orientation of the electron beam. On the other hand, when the interface is tilt relative to the emission orientation of the electron beam, since the interface portion is obliquely projected, the interface portion is observed in a manner of spreading in a tilt orientation in the observation image, and therefore it is difficult to clearly check the position. Accordingly, resolution of an acquired image changes according to a relationship between an orientation along which an electron beam is emitted and an orientation of a specimen.

A high-resolution image in which image bleeding is prevented is acquired by aligning the interface in the specimen structure in a traveling orientation of the electron beam to be emitted. A method for acquiring such a condition utilizes a matter that an orientation of the interface in the specimen structure and an orientation (a crystal orientation) of a crystal of a substrate portion coincide with each other in many cases in a semiconductor device specimen or the like formed on a crystal substrate. A tilt orientation of the entire specimen is adjusted so that the orientation of the crystal of the substrate portion coincides with an orientation of an emitted electron beam. A crystal orientation of a substrate portion of a specimen may be seen from an external appearance of the specimen. In the case of a specimen produced using a focused ion beam device, a crystal orientation inside the specimen differs from that seen from the external appearance, and cannot be determined from the external appearance. When the crystal orientation of the specimen cannot be determined from the external appearance, it is required to calculate a deviation amount and the orientation of the crystal orientation of the specimen using a diffraction pattern acquired by emitting an electron beam. At this time, when a region other than a crystal region of the substrate portion is included in a region illuminated with the electron beam, an acquired diffraction pattern is a mixture of a plurality of pieces of information, and it is difficult to calculate the deviation amount and the orientation of the crystal orientation. Therefore, the electron beam has a size that enables the electron beam to fall within the crystal region, and is emitted while being stopped at one position inside the crystal region, thereby acquiring a diffraction pattern.

For example, PTL 1 discloses a technique for detecting a diffraction pattern in a transmission charged particle microscope. By using a scanning assembly for inducing a relative motion between a diffraction pattern and a detector during recording of each frame, a maximum intensity value at each local position in the pattern draws a trajectory on the detector.

PTL 1: US2019/0057836

When a device slice specimen is observed using an STEM or a TEM, it is required to match a specimen orientation with an incident orientation of an electron beam at the time of observation in order to perform a length measurement with high accuracy. When the orientations deviate from each other, an interface is blurred and accuracy of the length measurement is lowered. The specimen orientation is adjusted by emitting an electron beam into a single crystal region serving as a reference in the specimen and changing specimen tilt while measuring deviation of the specimen orientation based on a diffraction pattern formed by the electron beam transmitted through the specimen.

During the adjustment work, since the electron beam is continuously emitted to a local region on the specimen, a decrease in crystallinity due to damage and specimen contamination are likely y to occur, and a failure in orientation adjustment and a decrease in accuracy may occur. Specifically, this can result in blurring of a diffraction pattern or disappearance of spots, and a clear diffraction pattern cannot be acquired. This is particularly likely to be a problem when a slice specimen such as a specimen of a semiconductor device manufactured by fine processing is observed or when a large current beam having a large convergence is used.

A representative example of the invention disclosed in the present application is as follows. That is, a charged particle beam device includes a movement mechanism configured to hold and move a specimen, a particle source configured to output a charged particle beam, a detector configured to detect a signal generated by illuminating the specimen with the charged particle beam, and a controller configured to control the movement mechanism, the particle source, and the detector. The controller determines an illumination target region in the specimen according to the specimen, moves an illumination position of the charged particle beam in the illumination target region, acquires a diffraction pattern according to a detection result of the detector at different illumination positions, and controls the movement mechanism based on an analysis result of the diffraction pattern to adjust tilt of the specimen.

According to an aspect of the invention, it is possible to reduce damage to a specimen to be observed in acquisition of a diffraction pattern for adjusting an orientation of the specimen. Problems, configurations, and effects other than those described above will be clarified by description of the following embodiments.

Hereinafter, an embodiment of the invention will be described with reference to the drawings. However, the invention is not to be construed as being limited to the description of the following embodiment. It will be easily understood by those skilled in the art that a specific configuration can be changed without departing from the spirit or scope of the invention.

In configurations of the invention to be described below, the same or similar configurations or functions are denoted by the same reference numerals, and redundant description will be omitted.

Notations “first”, “second”, “third”, and the like in the present description and the like are provided to identify components, and do not necessarily limit the number or the order.

In order to facilitate understanding of the invention, a position, a size, a shape, a range, and the like of each configuration shown in the drawings and the like may not represent an actual position, size, shape, range, and the like. Therefore, the invention is not limited to the position, the size, the shape, the range, and the like disclosed in the drawings.

In a charged particle beam device according to an embodiment of the present description, when a diffraction pattern for adjusting an orientation of a specimen to be observed is to be acquired, an illumination position is not fixed and an illumination region is widened by scanning a minute region with a charged particle beam (a primary beam or simply referred to as a beam). Dispersion of the illumination position reduces damage and contamination caused by a temperature rise or the like. Further, since information is averagely acquired due to dispersion of regions, it is possible to adjust an orientation more accurately. The diffraction pattern includes a spot pattern and Ronchigram.

The charged particle beam device determines a scanning region of the charged particle beam according to a target specimen. The scanning region is, for example, a single crystal region. For example, when the specimen is a semiconductor chip, a region in a silicon substrate can be selected as the scanning region. The charged particle beam device can acquire a fixed (the same) diffraction pattern even when the single crystal region is scanned with a beam. A deflected specimen can be adjusted to an average orientation.

is a view showing an example of a configuration of a scanning transmission electron microscope (STEM) according to an embodiment of the present description.

A STEMincludes an electron optical system columnand a control unit. The electron optical system columnincludes an electron source, first and second condenser lens, a condenser aperture, an axial deviation correction deflector, a stigmator, an image shift deflector, an objective lens, a specimen stage, an intermediate lens, a projection lens, an electron detector group, and a secondary electron detector. When the devices included in the electron optical system columnare not distinguished from one another, the devices are also referred to as target devices.

The specimen stageholds a specimen. The specimenmay be held by a specimen holder fixed to the specimen stage. The specimen stageor the specimen holder or a combination of the specimen stageand the specimen holder is an example of a movement mechanism that holds and moves the specimen. The specimen stagecan be tilted at one or more tilt axes (rotation axes).

An electron beam emitted from the electron sourcewhich is a particle source is reduced by the first and the second condenser lenses, and a radiation angle is limited by the condenser aperture. Further, after an axis of the electron beam is adjusted by the axial deviation correction deflector, the stigmator, and the image shift deflector, the electron beam is emitted in an orientation substantially perpendicular to the specimenby a specimen front side magnetic field of the objective lens.

The first and the second condenser lens, the condenser aperture, the axial deviation correction deflector, the stigmator, the image shift deflector, the objective lens, the specimen stage, the intermediate lens, and the projection lensare examples of an optical element that adjusts an orientation and a focus of the electron beam on the specimen.

The control unitis a controller, generates a secondary electron image indicating a surface structure of the specimenbased on secondary electrons detected by the secondary electron detector, and displays the secondary electron image to a user. Generally, in the STEM, a diffraction pattern is formed near a rear focus plane positioned between the objective lensand the intermediate lensdue to an influence of a rear magnetic field of the objective lens. The diffraction pattern is detected by the electron detector group(hereinafter, also simply referred to as the detector). The detectormay include an annular dark field-of-view detector, a bright field-of-view detector, a CCD camera, and the like. The detectordetects a signal emitted from the specimenilluminated with the electron beam.

A computer serving as the control unitcontrols the electron optical system columnusing a plurality of control circuits. The control unitincludes an electron gun control circuit, an illumination lens control circuit, a condenser aperture control circuit, an axial deviation correction deflector control circuit, a stigmator control circuit, an image shift deflector control circuit, an objective lens control circuit, a specimen stage control circuit, an intermediate lens control circuit, a projection lens control circuit, a transmission scattering detector control circuit, and a secondary electron detector control circuit.

The control unitacquires a value of each target device via each control circuit, and creates any electron optical condition by inputting the value to each target device via each control circuit. The control unitis an example of a control mechanism that controls the electron optical system column.

The control unitincludes a processor, a main storage device, an auxiliary storage device, an input device, an output device, and a network interface. These devices are connected to one another via a bus.

The processorexecutes a program stored in the main storage device. The processorfunctions as various functional units by executing processing according to programs.

The main storage deviceis a storage device such as a semiconductor memory, and stores a program and data executed by the processor. The main storage deviceis also used as a work area for temporary use of programs. The main storage devicestores, for example, an operating system, a program for controlling a target device of the STEM, a program for acquiring an image of the specimen, and a program for processing the acquired image.

In the present description, when processing is described using the STEM(the control unit) as a subject, it indicates that the processorthat executes any one of the programs is executing the processing.

The auxiliary storage deviceis a storage device such as a hard disk drive (HDD), a solid state drive (SSD), or the like, and permanently stores data. A program and data stored in the main storage devicemay be stored in the auxiliary storage device. In this case, when the control unitis start up or when processing is required, the processorreads a program and data from the auxiliary storage deviceand loads the program and the data into the main storage device.

The input deviceis a device for a user to input instructions and information to the control unit, such as a keyboard, a mouse, and a touch panel. The output deviceis a device for outputting an image, an analysis result, and the like to a user, such as a display and a printer. The network interfaceis an interface for performing communication via a network.

Although the control unitis described as a computer in, the control unitmay be implemented using a plurality of computers. Some functions of the control unitmay be implemented by using a logic circuit such as an ASIC or an FPGA that is configured for specific processing. Primary charged particles emitted to the specimenmay be different from electrons.

The STEMilluminates the specimenwith a converged electron beam, and scans the specimenwith the converged electron beam using a deflection coil such as the image shift deflector. The detectorrecords a signal detected by the detector at each scanning position on the specimen, and the control unitdisplays an image. The detectormay include a plurality of types of detectors such as an annular dark field-of-view detector, an annular bright field-of-view detector, a bright field-of-view detector, and a CCD camera. A desired type of image can be acquired by detecting transmitted or scattered electron by a detector selected according to lens adjustment below the specimen.

is a flowchart showing an outline of processing executed by the STEM. The STEMautomatically adjusts the specimen stageso that deviation between an orientation of the specimenand an incident orientation of an electron beam to the specimenis minimized.

When the specimenis observed by the STEM, a length measurement can be performed with high accuracy by matching an electron beam incident orientation and a specimen orientation at the time of observation. When the specimen orientation deviates from the electron beam incident orientation, an interface is blurred and accuracy of the length measurement is reduced. The specimen orientation is adjusted using a diffraction pattern formed by the electron beam transmitted through the specimen. The STEMchanges tilt of the specimen while measuring a deviation amount of the specimen orientation based on the diffraction pattern.

In order to acquire the diffraction pattern, the STEMscans a specific region of the specimenwith the electron beam. When the diffraction pattern for orientation adjustment is acquired, an illumination region is widened by performing scanning with the electron beam in a target region, and damage and contamination of the specimencan be reduced.

In an embodiment of the present description, a single crystal region (hereinafter, simply referred to as a crystal region) in the specimenis selected as a target region for acquiring a diffraction pattern. For example, in a semiconductor device, n substrate is generally formed of single crystal silicon, and has a sufficient width for reducing damage. In an example to be described below, the STEMscans a region in the silicon substrate of the specimenwith an electron beam to acquire a diffraction pattern.

Referring to, the control unitdetermines an illumination target region for acquiring a diffraction pattern in the specimen(S). Details of a method for specifying the illumination target region will be described later. Next, the control unitscans the illumination target region determined in step Swith an electron beam to acquire a diffraction pattern (S).

Next, the control unitdetermines a deviation amount of an orientation of the specimenfrom an electron beam incident orientation based on the diffraction pattern (S). Further, the control unitcontrols the specimen stageto adjust tilt of the specimenbased on the orientation deviation amount determined in step S(S). Accordingly, a crystal orientation of the specimen can be aligned with an incidence angle of the electron beam, and the deviation can be minimized. If possible, the incidence angle of the electron beam may be adjusted instead of controlling the tilt of the specimen.

Hereinafter, the method (S) for determining the illumination target region for acquiring a diffraction pattern for orientation adjustment in the specimenwill be described. Here, the control unitselects a single crystal region as the illumination target region. Any region in the specimenwhere a diffraction pattern can be acquired can be selected as the illumination target region.

A region to be specified as the illumination target region and a specifying method of the illumination target region are specified for each specimen, and the STEMdetermines the illumination target region according to the specimen. In one embodiment, the control unitmay refer to specimen information including specimen structure information and determine a region having a size and a shape indicated by the specimen information as the illumination target region. In one embodiment, the control unitmay refer to a signal acquired by illuminating the specimenwith an electron beam and determine a region of a specified substance state as the illumination target region. An example of the specified substance state is a single crystal structure.

is an observation image schematically showing an example of an overall external appearance including a semiconductor specimen and a support structure of the semiconductor specimen.shows a secondary electron image. In, the semiconductor specimenincludes a rectangular slice regionand support portions(only one of the support portions is indicated by a reference numeral) on both sides. The support portionis coupled to a base portionon a lower side in. In, the slice regionis, for example, a region of the semiconductor specimenthat is sliced by being illuminated with a converged ion beam from an orientation of an upper side of the drawing. The support portionis a region that is not sliced and has a thickness. The base portionis also a region having a thickness.

Since the electron beam is transmitted through the slice regionof the semiconductor specimen, the slice regionis an observable region. The observable region is a region in the specimen where the electron beam is transmitted (including straight electrons and scattered electrons). On the other hand, the support portionand the base portionhaving a thickness cannot let the electron beam transmit and are unobservable regions. Other regions inare spaces (vacuum regions) where no substance is present. The electron beam is not scattered in the vacuum regions and is transmitted. The vacuum region is an observable region, and is a non-single crystal region (also simply referred to as a non-crystal region) to be described later in the present description. Hereinafter, the slice region of the semiconductor specimen is also referred to as a semiconductor slice specimen.

The control unitacquires a secondary electron observation image or a STEM observation image of the specimen. For example, the specimen stageis moved by pattern matching so that an initial position (an initial illumination position)is located near the center of the field of view.is a partially enlarged view showing an observation image of the semiconductor slice specimen. The semiconductor slice specimen (the observable region)includes a substrate regionmade of single crystal silicon and an element region (a structure region)on the substrate region. The element regionis a non-single crystal region. In the present example, the initial positionis located substantially at the center of the substrate region.

The control unitdetermines an illumination target regionin the substrate region. The control unitacquires a diffraction pattern while scanning the specimen. The control unitsearches for a region where the diffraction pattern does not change from the initial position, and determines the region as the illumination target region.

shows an example of a diffraction pattern acquired by emitting an electron beam to a single crystal region. The specimen includes a single crystal regionand a non-single crystal region. An electron beamis emitted to the single crystal region. The same diffraction pattern can be acquired regardless of an illumination position in the single crystal region. An acquired diffraction patternincludes a plurality of spots arranged regularly in a two-dimensional manner. By performing region recognition (a blob analysis or the like) of the diffraction pattern, a diffraction patternin which each spot can be clearly determined is acquired. In the blob analysis, the diffraction patternis binarized to determine an outer shape of each spot.

shows an example of a diffraction pattern acquired by emitting an electron beam to a non-single crystal region. The electron beamis emitted to the non-single crystal region. An acquired diffraction patternincludes one spot. By performing region recognition (a blob analysis) of the diffraction pattern, a diffraction patternin which the spot can be clearly determined is acquired. In the blob analysis, the diffraction patternis binarized to determine an outer shape of each spot.

As shown in, the diffraction patternof the single crystal region and the diffraction patternof the non-single crystal region have different pattern shapes. The pattern acquired from the single crystal region includes a plurality of periodic diffraction spots corresponding to a crystal structure. The pattern acquired from the non-single crystal region includes only one spot through which the beam is transmitted.

As described above, the control unitacquires a list indicating coordinates, a size, and the like of each spot by performing the binarization processing and the blob analysis. The control unitmay determine the illumination target region by evaluating the number of diffraction spots for a diffraction pattern acquired at an illumination position to be evaluated. For example, when the number of spots in a pattern is less than one or less than a reference number, the control unitcan determine a region as the non-single crystal region. When the number of spots is larger than a reference number, the control unitcan determine a region as the single crystal region.

In another example, the control unitcan detect a boundary between the single crystal regionand the non-single crystal regionby moving an illumination position of the electron beam and comparing a diffraction pattern acquired at each position with a diffraction pattern acquired at an initial position. For example, the single crystal regionand the non-single crystal regioncan be distinguished by comparing a position, a size, the number, or the like of each spot in a diffraction pattern acquired by performing the blob analysis on the diffraction pattern acquired at each position and the diffraction pattern acquired at the initial position.

The control unitmay evaluate similarity between the diffraction pattern acquired at the initial position which is a reference illumination position and a diffraction pattern acquired at an illumination position to be evaluated. The control unitcalculates the similarity between the two diffraction patterns, and determines a position where the similarity is a threshold as a boundary between illumination target regions.

The similarity between the two patterns can be calculated, for example, based on match or mismatch of luminance values of pixels of the diffraction patterns. When the total number of pixels whose luminance value difference exceeds a predetermined reference is smaller than a threshold, it may be determined that two diffraction patterns similar. A method for calculating the similarity between diffraction patterns can be determined appropriately by design. The blob analysis enables a more accurate comparison, but may be omitted.